How did scientists arrive at a figure for the speed of light?

Galileo, the famous Italian scientist, made an attempt to measure the speed of light in the 1630's, but all he could prove was that light traveled very fast.

In 1728, an English astronomer, James Bradley , calculated the speed of light from the direction in which light fell from a star to Earth. He came up with a figure of 301,1000 kilometers per second. In 1849, another scientist, Fizeau, improved on Bradley's calculations, and came up with a new figure: 313,300 kilometers per second.

In 1923, Albert Michael son changed the figure for the speed of light. He said it was nearly 299,798 kilometers per second. In 1970's the speed of light was officially approved to be 299,792.458 kilometers per second.